The background of the invention will be set forth in two parts as follows:
1. Field of the Invention
The invention relates to the field of lighting fixtures in general and to lighting fixtures that have hood assemblies which are adjustable with respect to the surface upon which they are mounted in particular.
2. Description of the Prior Art
In lighting applications, where a large working surface such as a drafting board or an electronic assembly bench is to be illuminated, one of the problems encountered is the difficulty of providing uniform illumination of the working surface. This problem is particularly acute in the case of drafting boards where the length of the board may exceed 10 feet. Also, the orientation of the board may change and disturb the uniformity of the illumination.
In the past light fixtures of various designs have been used to provide the desired lighting intensity on the working surface, particularly when the overhead lighting such as found in drafting rooms do not provide sufficient light intensity on the working surface. These light fixtures are either mounted directly on the working surface or mounted in the vicinity of the working surface. Typical of these devices are Trombolite Fixtures, manufactured by Fostoria Industries, Inc., The Floating Arm Fluorescent Lamp Fixture, manufactured by Dazor Manufacturing Corporation; the FL series fluorescent lamp and the B series lamp both of which are manufactured by Luxo Company.
Although all the foregoing devices allow for adjustment of the position of the light source with respect to the working surface, none of them provide a uniform illumination of the working surface, particularly large working surfaces. The Trombolite fixtures and the B series lamps utilize incandescent light sources housed in circular hoods whose inner surfaces function as reflectors. A concentrated cone of light is emitted which tends to illuminate only a relatively small area.
The Floating Arm fixture and the FL series lamp both utilize fluorescent light sources housed in a logitudinal hood assembly which also acts as a reflector. The illumination provided by these devices tends to be more uniformly distributed than those where the light source is a conventional light bulb and a circular hood is used as the reflector. However, because the length of the fluorescent lamps extend only over a fraction of the length of the working surface, the desired uniform illumination is not provided.
A lighting appliance, invented by L. C. Doane (U.S. Pat. No. 2,092,573) contains a hood assembly which extends over the entire length of the surface to be illuminated. The Doane device is, however, limited as to length of the hood assembly, because the excessive weight of a long assembly coupled with the additional weight required by the arm pivot system which utilize a strap device for the pivot system. The difficulty in supporting the excessive weight required by very long hood assemblies with a suitable pivot joint system is typical of prior art fluorescent light fixtures including the Doane device.
As previously indicated, another problem with most prior art light fixtures, including the Doane device, is that the uniformity of illumination is disturbed with a change in orientation of the working surface. The orientation of hood assembly is upset when the working surface is rotated or translated, as in the case of modern drafting tables, which have the capability of rotating the working surface to a vertical position plus the capability of adjusting the height of the work surface. The Trombolite fixture attempts to provide the capability of maintaining the position of the light source independent of the orientation of the working surface, by mounting the device on a horizontal arm of the drafting machine. The disadvantage of this device is that the lamp travels together with the arm of the drafting machine and tends to upset the adjustment of the drafting machine when the lamp is adjusted to various positions. This adjustment is necessary because of the limited area of the illumination provided by this device.